1. Field of the Invention
The present invention relates to a heat exchanger used for a refrigerating cycle composed of a compressor, etc.
2. Description of the Related Art
Hitherto, a heat exchanger used for the electric equipment for refrigeration or air conditioning (such as an air conditioner, a freezer, and a cooled showcase) is constructed with a refrigerant pipe which forms a refrigerating cycle and has a plurality of fins as disclosed in, for example, Japanese Patent Publication No. 4-16711 (F28G9/00).
The fins are designed to pen-it efficient dissipation or absorption of heat between the refrigerant, which flows through the refrigerant pipe, and air. They are usually made of aluminum sheet which is approximately 100 to 120 microns thick.
When such a heat exchanger is used as a condenser for a refrigerating cycle, for example, a gas refrigerant of high temperature and high pressure which is discharged from a compressor flows into the heat exchanger, causing the temperature thereof to go up to approximately +20 to +100 degrees centigrade. The heat of the refrigerant is transferred from the refrigerant pipe wall of the heat exchanger or the condenser to the fins and it is radiated into the air from the surfaces of the fins, a part thereof being radiated from the surfaces of the refrigerant pipe.
The refrigerant radiates heat and condenses from such heat radiation. The surfaces of the fins of the conventional heat exchanger are provided with transparent hydrophilic coating after they are washed; therefore, the color of the surfaces is silver, which is extremely close to white (hereinafter referred to as "white").
The white color has high reflectance of light and therefore lowers the heat conductivity based on the wavelength of reflected light, i.e. heat ray, making it difficult to improve the heat radiation of the fins. Thus, the heat radiation from the fins is lowered, thus adversely affecting the condensation of the refrigerant in the heat exchanger. This adds to the difficulty in achieving an improved cooling capability of the refrigerating cycle.
Although the aforesaid problem is not as remarkable as in the case of a condenser, the same problem is observed when the heat exchanger is used for a cooler or evaporator. More specifically, as the reflectance of light increases, the absorption of heat by the ambient air deteriorates.
A means for improving the performance of a heat exchanger has been disclosed in, for example, Japanese Patent Publication No. 4-21117 (F28F1/40). According to the disclosure, the inner surface of a refrigerant pipe is provided with many helical grooves, so that a refrigerant flows along the grooves from the capillary action all the way up to the top of the pipe to ensure heat exchange between the refrigerant and the refrigerant pipe over an extended area, or over the entire area ideally, of the inner surface of the pipe, thereby improving the heat transfer characteristic.
When a refrigerant composed of a mixture of two or more types of refrigerants is used as the refrigerant flowing through the refrigerant pipe, the respective ingredient refrigerants exhibit different properties, especially different viscosities. The grooves in the conventional refrigerant pipe, however, all had the same width; therefore, when the refrigerant is in the gas-liquid mixture condition and the rate of flow liquid in the refrigerant is small, setting the grooves to a small width for a refrigerant with low viscosity presents a problem in that the width is too small for a refrigerant with high viscosity and the flow resistance increases, leading to a large pressure loss. The result is stagnation of the refrigerant with high viscosity. Conversely, setting the grooves to a larger width so as to match it to a refrigerant with high viscosity poses a problem in that the grooves are too wide for a refrigerant with low viscosity and the capillary action no longer works.